Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.5.1.18 (glutathione S-transferase)
 22,582 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The mitochondrial outer membrane enzyme kynurenine 3-hydroxylase (K3H) is an NADPH-dependent flavin mono-oxygenase involved in the tryptophan pathway, where it catalyzes the hydroxylation of kynurenine. K3H was transiently expressed in COS-1 cells as a glutathione S-transferase (GST) fusion protein, and the pure recombinant protein (rec-K3H) was obtained with a specific activity of about 2000 nmol.min-1.mg-1. Rec-K3H was shown to have an optimum pH at 7.5, to use NADPH more efficiently than NADH, and to contain one molecule of non-covalently bound FAD per molecule of enzyme. The mechanism of the rec-K3H-catalyzed reaction was investigated by overall initial-rate measurements, and a random mechanism in which combination of the enzyme with one substrate does not influence its affinity for the other is proposed. Further kinetic studies revealed that K3H activity was inhibited by both pyridoxal phosphate and Cl-, and that NADPH-catalyzed oxidation occurred even in the absence of kynurenine if 3-hydroxykynurenine was present, suggesting an uncoupling effect of 3-hydroxykynurenine with peroxide formation. This observation could be of clinical interest, as peroxide formation could explain the neurotoxicity of 3-hydroxykynurenine in vivo.
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PMID:Functional characterization and mechanism of action of recombinant human kynurenine 3-hydroxylase. 1067 18

Mammalian serine hydroxymethyltransferase (SHMT) is a tetrameric, pyridoxal phosphate-dependent enzyme that catalyzes the reversible interconversion of serine and tetrahydrofolate to glycine and methylenetetrahydrofolate. This reaction generates single-carbon units for purine, thymidine, and methionine biosynthesis. Cytoplasmic SHMT (cSHMT) has been postulated to channel one-carbon substituted folates to various folate-dependent enzymes, and alternative splicing of the cSHMT transcript may be a mechanism that enables specific protein-protein interactions. The cytoplasmic isozyme is expressed from species-specific and tissue-specific alternatively spliced transcripts that encode proteins with modified carboxy-terminal domains, while the mitochondrial isozyme is expressed from a single transcript. While the full-length mouse and human cSHMT proteins are 91% identical, their alternatively spliced transcripts differ. The murine cSHMT gene is expressed as two transcripts. One transcript encodes a full-length 55 kDa active enzyme (cSHMT), while the other transcript encodes a 35 kDa protein (McSHMTtr). The McSHMTtr protein present in mouse liver and kidney does not bind 5-formyltetrahydrofolate, nor does it oligomerize with the full-length cSHMT enzyme. While recombinant cSHMT-glutathione S-transferase fusion proteins form tetramers and are catalytically active, McSHMTtr-glutathione S-transferase fusion proteins are catalytically inactive, do not form heterotetramers, and do not bind pyridoxal phosphate. Analysis of the murine cSHMT crystal structure indicates that the active site lysine that normally binds pyridoxal phosphate in the cSHMT protein is exposed to solvent in the McSHMTtr protein, preventing stable formation of a Schiff base with pyridoxal phosphate. Modeling studies suggest that the human cSHMT proteins expressed from alternatively spliced transcripts are inactive as well. Therefore, channeling mechanisms enabling specific protein-protein interactions of active enzymes are not based on cSHMT alternative splicing.
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PMID:Lack of catalytic activity of a murine mRNA cytoplasmic serine hydroxymethyltransferase splice variant: evidence against alternative splicing as a regulatory mechanism. 1130 8

In this work, we report that the recombinant glutathione S-transferase (GST)-human L-glutamic acid decarboxylase (HGAD) isoforms, 65-kDa L-glutamic acid decarboxylase (GAD) (GST-HGAD65) fusion protein or free truncated HGAD65, were activated by apocalmodulin (ApoCaM) to an extent of 60%. Both truncated forms of GAD67 (tGAD67), HGAD67(Delta1-70) and HGAD67(Delta1-90), were markedly activated by ApoCaM to an extent of 141 and 85%, respectively, while GST-HGAD67 was not significantly affected. The activation appears to be due to an increase of GAD affinity for its cofactor, pyridoxal phosphate (PLP). This conclusion is based on the following observations. Firstly, the V(max) of GAD was increased when ApoCaM was present whereas the affinity for the substrate, glutamate, was not affected. Secondly, the affinity of GAD for PLP was increased in the presence of ApoCaM. Thirdly, results from calmodulin-agarose affinity column chromatography studies indicated a direct interaction or binding between ApoCaM and GAD. Fourthly, ApoCaM was found to be copurified with GAD65/GAD67 by anti-GAD65/67 immunoaffinity column using rat brain extract. Hence, it is proposed that a conformational change is induced when ApoCaM interacts with GAD65 or tGAD67, resulting in an increase of GAD affinity for PLP and the activation of GAD. The physiological significance of the interaction between GAD and ApoCaM is discussed.
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PMID:Effect of apocalmodulin on recombinant human brain glutamic acid decarboxylase. 1568 75

The aim of this study was to examine the efficacy of vitamin B6 against chromium (Cr)-induced oxidative stress. Adult male albino Wistar rats (100-120 g) were used in this study. Potassium dichromate, a Cr VI compound, was administered at a dose of 127 mg kg(-1) p.o. Vitamin B6 (pyridoxine hydrochloride) was administered at a dose of 100 mg kg(-1) p.o. either alone or 12 h prior to Cr or simultaneously with Cr. Chromium treatment induced oxidative stress in the liver as measured by increased lipid peroxidation (LPO) and decreased vitamin C, vitamin E, glutathione (GSH), glutathione peroxidase (GPX), catalase (CAT), superoxide dismutase (SOD), glutathione S-transferase (GST) and glutathione reductase (GR). Both pre- and simultaneous treatments countered Cr-induced oxidative stress; pre-treatment was more effective than concurrent administration. The results demonstrate the antioxidant potential of vitamin B6.
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PMID:Protective effect of vitamin B6 in chromium-induced oxidative stress in liver. 1598 93

Although vitamin B6 has been supposed to have anti-inflammatory effects, the molecular mechanism is not fully understood. To explore the mechanism of anti-inflammatory effects of vitamin B6, we have examined the effect of vitamin B6 on lipopolysaccharide (LPS)-stimulated inflammatory response in RAW 264.7 macrophages. This study demonstrated that vitamin B6 (pyridoxal) pretreatment of RAW cells inhibited LPS-induced expression of iNOS and COX-2 at the mRNA and protein levels. Vitamin B6 inhibited LPS-induced nuclear translocation of the NF-kappaB, the proinflammatory transcription factor, with reduction of the extent of LPS-induced IkappaBalpha degradation in RAW cells. Although vitamin B6 did not affect cellular proteasome activity, in vitro phosphorylation analysis with glutathione S-transferase-fused IkappaBalpha has shown that vitamin B6 suppressed LPS-induced IkappaB kinase activation. Furthermore, we demonstrated that elevating dietary vitamin B6 suppressed NO production in vivo in response to LPS administration. These observations suggest that the anti-inflammatory effect of vitamin B6 is mediated by suppression of NF-kappaB activation.
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PMID:Vitamin B6 suppresses NF-kappaB activation in LPS-stimulated mouse macrophages. 1627 88